Multi-channel current probe

ABSTRACT

A current probe for measuring electrodeposition plating currents. The current monitoring probe includes a conductive layer located on a front face of the current monitoring probe, an insulating layer behind the conductive layer, and a plurality of current sensing circuits located behind the insulating layer. The insulating layer isolates the current sensing circuits from the conductive layer. A plurality of apertures are formed through the conductive layer and the insulating layer, each aperture exposing one of the plurality of current sensing circuits to metal ions incident to the aperture.

FIELD

The present invention relates to a system and method for monitoring andadjusting fields associated with the electrodeposition of a metal onto asurface. More particularly, the present invention relates to a systemfor monitoring the spatial variation of the current and current densityto obtain a desired thickness of electroplated metal.

BACKGROUND

Electrodeposition of a metal onto a surface has many applications. Onesuch application is the deposition of a metal, typically copper, onto aflexible substrate in order to create interconnects on the flexiblesubstrate. Interconnects are essentially low-resistance transmissionlines with precisely controlled propagation characteristics. In order tocontrol these propagation characteristics, the thickness of the metalplating must be precisely controlled. Typically, this requires that theelectroplated metal be deposited in uniform layers onto the flexiblesubstrate. Uniformity of electrodeposited layers is influenced by thedesign and adjustment of the plating system, including the currentdistribution seen by the flexible substrate. If the current distributionis uneven across the flexible substrate, then the plating thickness willalso be uneven.

Typical methods of testing and measuring plating uniformity includeplacing a substrate through the electroplating machine, running theelectroplater for an amount of time, removing the substrate from theelectroplating machine, and measuring thickness variation using an X-rayfluorescence machine. The plating machine is adjusted based on theresults of the X-ray fluorescence machine, and another trial is rununtil the desired distribution is determined. However, this iterativemethod of plating and measuring is both costly and time-consuming.

SUMMARY

In one aspect, the present invention provides a current probe formeasuring local electrodeposition plating currents. The current probecomprises a conductive layer located on a front face of the currentprobe, an insulating layer located adjacent to the conductive layer, anda plurality of current sensing circuits located adjacent to theinsulating layer, wherein the insulating layer is located between theconductive layer and the plurality of current sensing circuits. Aplurality of apertures are formed through the conductive layer and theinsulating layer, wherein each of the plurality of apertures exposes oneof the plurality of current sensing circuits.

Another aspect of the present invention provides for anelectrodeposition monitoring system. The monitoring system is comprisedof a plating cell for holding a metal salt bath, an electrode located inthe plating cell, a probe having a plurality of current sensingcircuits, wherein each of the plurality of current sensing circuitssenses a local electrodeposition plating current, and a computer systemconnected to the probe that determines an electrodeposition platingthickness based on the local electrodeposition plating currents sensedby the plurality of current sensing circuits.

A further aspect of the present invention provides a method of providingreal time analysis of electrodeposition plating currents. The methodincluding placing a multi-channel current probe in a plating cell,generating an electrodeposition plating current, measuring theelectrodeposition plating current at a plurality of locations on themulti-channel current probe using a plurality of current sensingcircuits and adjusting the distribution of the electrodeposition platingcurrents based on the measurements taken.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an exemplary embodiment of an electrodepositionmeasurement system.

FIG. 2A is a front view of an exemplary embodiment of a current probeused in the current probe measurement system.

FIG. 2B is a back view of an exemplary embodiment of the current probe.

FIG. 3 is a cross-sectional view of an exemplary embodiment of thecurrent probe.

FIG. 4 is a diagram of an exemplary embodiment of a single channelwithin the current probe.

DETAILED DESCRIPTION

FIG. 1 shows an exemplary embodiment of electrodeposition measuringsystem 10, which includes plating cell 12, plating bath 14 containedwithin plating cell 12, electrode 16, current probe 18 which includes aplurality of apertures 20 a, 20 b, . . . 20N (“apertures 20”), plasticbaffles 22 a and 22 b, data acquisition board 23, and computer system24.

To measure the spatial distribution of plating currents, current probe18 is placed in plating cell 12, submerged in plating bath 14. In thisexemplary embodiment, plating bath 14 includes copper ions (Cu²⁺). Apotential difference is created between electrode 16 (which in thisexemplary embodiment, acts as an anode) and current probe 18 (which inthis embodiment acts as a cathode). The potential difference causescopper ions (Cu²⁺) located in plating bath 14 to flow toward currentprobe 18. Copper ions flowing toward current probe 18 eventually comeinto contact with current probe 18, where the ionic charge isneutralized and the copper ions plate onto the surface of current probe18. The flow of positive charge to current probe 18 caused by the copperions results in current being generated at current probe 18. Themagnitude of the current, and more specifically of current density, isdirectly related to the thickness of copper plating deposited on currentprobe 18. Variations in current density across the area of current probe18 result in varying plating thickness. By detecting and measuringcurrent magnitude and/or current density at a number of locations alongcurrent probe 18, the plating thickness at each location can bedetermined.

In an exemplary embodiment, current associated with copper ions incidentto the plurality of apertures 20 is detected by current sensingcircuits, the details of which are described below with respect to FIG.2B. Currents detected at the plurality of apertures 20 are provided todata acquisition board 23. Data acquisition board 23 measures currentsdetected at the plurality of apertures 20 by measuring a voltage dropacross each current sensing circuit. The measured current valueassociated with each of the plurality of apertures 20 is converted bythe data acquisition board to a digital value, which can be displayed orstored by computer system 24. Knowing the area of each aperture 20 (inone embodiment, each aperture 20 is of equal area) allows either dataacquisition board 23 or a processor to calculate current densityassociated with each aperture 20. In this way, electrodepositionmeasuring system 10 provides real time data concerning current and/orcurrent density sensed at a number of locations along current probe 18.Based on this data, a user can manipulate the mechanics of plating cell12 or plating bath 14 to achieve the desired current distribution alongcurrent probe 18. In the exemplary embodiment shown, plastic baffles 22a and 22 b may be manipulated to alter the current distribution. Currentdistribution can be measured again using current probe 18, and furtheradjustments can be made.

FIGS. 2A-2B are diagrams of the front and back faces, respectively, ofcurrent probe 18. FIG. 2A shows conductive layer 26 located on the frontface of current probe 18, along with a plurality of apertures 20 a, 20b, . . . 20N (“apertures 20”). Conductive layer 26 acts as an electrode(in this example, a cathode) in the electrodeposition process. Duringtesting of electrodeposition current distribution, a potentialdifference is created between conductive layer 26 and electrode 16(shown in FIG. 1), causing metal ions to travel toward conductive layer26. Connector tabs 28 a and 28 b, discussed in more detail below, may beconnected to a power supply capable of providing a potential toconductive layer 26. Apertures 20 are small openings in conductive layer26 that extend through conductive layer 26 (as well as an insulatinglayer shown in FIG. 3) to one of the plurality of current sensingcircuits 32 a, 32 b, . . . 32N. (“current sensing circuits 32”) formedon the back face of current probe 18, as shown in FIG. 2B. Metal ionsincident to apertures 20 travel through the apertures and plate ontocurrent sensing circuits 32. The current created at each of the currentsensing circuits 32 by incident metal ions allows current probe 18 todetermine the magnitude and/or density of current at each of theplurality of apertures 20.

FIG. 2B is a diagram of the back face of current probe 18, including aplurality of current sensing circuits 32 a, 32 b, . . . 32N, depositedon an insulating layer 34. A current measuring device 35 (in oneembodiment, current measuring device 35 is included within dataacquisition board 23 (FIG. 1)) connects to probe 18 by way of connectortabs 28 a and 28 b. In this embodiment, there are eight current sensingcircuits, each providing a channel of data to current measuring device35. Each current sensing circuit 32 intersects with one of the pluralityof apertures 20 shown in FIG. 2A and is extended to the edge ofconnector tabs 28 a and 28 b. Current measuring device 35 is connectedbetween connector tabs 28 a and 28 b, which closes the circuit betweenpoints A and B for each current sensing circuit 32 and allows currentmeasuring device 35 to measure current by determining a voltage dropbetween points A and B.

Insulating layer 34 isolates current sensing circuits 32 from conductivelayer 26 located on the front face of current probe 18. Therefore,apertures 20 are formed through conductive layer 26 as well asinsulating layer 34 to expose a conductive portion of current sensingcircuit 32 to incoming metal ions. In order for the sensing circuits 32to sample representative plating currents on electrode 26, currentsensing circuits 32 are held at nearly the same cathodic potential aselectrode 26. Current generated in each of the current sensing circuits32 by incoming metal ions is provided to current measuring device 35.

The conductive lines (having a thickness and depth) making up eachcurrent sensing circuit 32 are formed by pattern plating copper ontoinsulating layer 34. As shown in FIG. 2B, the conductive line length ofeach current sensing circuit 32 varies depending on the distance toconnector tabs 28 a and 28 b. This varying length of each currentsensing circuit 32 can result in varying overall resistance values ofeach current sensing circuit 32. For example, the conductive line lengthof current sensing circuit 32 a is shorter than the conductive linelength of current sensing circuit 32 b, which results in current sensingcircuit 32 a having a lower overall resistance than current sensingcircuit 32 b. Varying overall resistances of each current sensingcircuit 32 must be taken into account when current measuring device 35measures the voltage drop between points A and B.

In one exemplary embodiment, the conductive line of each of the numberof current sensing circuits 32 is designed such that each currentsensing circuit 32 is of equal resistance. By varying the thicknessand/or width of the conductive lines making up each current sensingcircuit 32, the overall resistance of each current sensing circuit 32can be made equal. Configuring current sensing circuits 32 to have equaloverall resistance allows for easier measuring and comparison ofcurrents by current measuring device 35. For instance, if currentsassociated with each current sensing circuit 32 are determined bymeasuring a voltage drop between points A and B, then the measuredvoltages can be directly compared without having to employ externalresistors to take into account the differences in resistance of currentsensing circuits 32.

FIG. 3 is a cross sectional view taken along dashed line 37 in FIG. 2B,illustrating the locations of conductive layer 26, insulating layer 34,current sensing circuit 32 a, and epoxy layer 36 within a portion ofcurrent probe 18. The resistance of current sensing circuit 32 a is madesufficiently small so that conductive layer 26 and current sensingcircuit 32 a are at nearly the same cathodic potential. Aperture 20 a isformed through conductive layer 26 and insulating layer 34 to exposecurrent sensing circuit 32 a to incident or incoming metal ions (e.g.,Cu²⁺). Insulating layer 34 separates conductive layer 26 from currentsensing circuit 32 a. Epoxy layer 36 prevents current incident to theback face of current probe 18 from affecting current sensing circuit 32a. During the measuring process, metal ions will plate onto currentsensing circuit 32 a. However, this does not have any significant effecton the overall resistance of current sensing circuit 32 a, and thereforedoes not affect current magnitude or density measurements. Therefore, asingle current probe 18 can be used a number of times to measure currentmagnitude and/or density distribution despite some amount of metalplating being deposited on each of the number of current sensingcircuits 32, provided metal plating deposited on current sensing circuit32 a does not extend up to conductive layer 26, resulting in a shortcircuit condition.

FIG. 4 is a schematic diagram of current sensing circuit 32 a located oncurrent probe 18. Current sensing circuit 32 a includes current sensingarea 40 a and conductive line 42 a and 42 b, which provides sensedcurrents to current measuring device 35 connected between connectingtabs 28 a and 28 b. It should be noted that each current sensing circuit32 a-32N will include similar current sensing area and conductive lineconnecting the current sensing area to connector tabs 28 a and 28 b.Aperture 20 a is formed through conductive layer 26 (shown in FIG. 3)and insulating layer 34 (shown in FIG. 3) to expose a portion of currentsensing area 40 a to incident currents. It is important that the areaexposed by aperture 20 a be entirely within current sensing area 40 a.If a portion of aperture 20 a exposes an area outside of current sensingarea 40 a, any current incident to this outside area will not generatecurrent within current sensing circuit 32 a. Knowing the amount ofcurrent sensing area 40 a exposed by aperture 20 a allows currentdensity to be determined along with the magnitude of the currentmeasured. If each of the plurality of current sensing circuits 32employed have an equal amount of current sensing area exposed, thencurrent densities of each can be compared without the need foradditional compensation or calculations.

A multi-channel current probe has been described. Although the currentprobe described with reference to FIGS. 1-4 is a current probe witheight apertures and corresponding current sensing circuits located invertical fashion, it should be understood that any number of aperturesand corresponding current sensing circuits may be employed and may belocated in any pattern order to gather information relevant to aparticular application.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

1. A current probe for measuring electrodeposition plating currents, thecurrent probe comprising: a conductive layer located on a front face ofthe current probe; an insulating layer located adjacent to theconductive layer; a plurality of current sensing circuits locatedadjacent to the insulating layer, wherein the insulating layer islocated between the conductive layer and the plurality of currentsensing circuits; and a plurality of apertures formed through theconductive layer and the insulating layer, wherein each of the pluralityof apertures exposes one of the plurality of current sensing circuits.2. The current probe of claim 1, wherein the plurality of currentsensing circuits have equal overall resistance.
 3. The current probe ofclaim 1, wherein each of the plurality of current sensing circuitsincludes: a current sensing area, a portion of which is exposed by oneof the plurality of apertures formed through the conductive layer andthe insulating layer; and a conductive line connecting the currentsensing area to a current or voltage measuring device.
 4. The currentprobe of claim 3, wherein each of the plurality of apertures exposes anequal amount of the current sensing area.
 5. The current probe of claim1, including an epoxy layer formed adjacent to the plurality of currentsensing circuits opposite the insulating layer, the epoxy layer locatedon a back face of the current probe.
 6. The current probe of claim 1,wherein the conductive layer consists of copper.
 7. The current probe ofclaim 1, wherein the insulation layer consists of polyimide.
 8. Thecurrent probe of claim 3, wherein the conductive line and the currentsensing area of each of the plurality of current sensing circuitsconsists of copper.
 9. An electrodeposition measuring system,comprising: a plating cell for holding a metal salt bath; an electrodelocated in the plating cell; a current probe having a plurality ofcurrent sensing circuits, wherein each of the plurality of currentsensing circuits senses a local electrodeposition plating current; and acomputer system connected to the current probe that determines anelectrodeposition plating thickness based on the local electrodepositionplating currents sensed by the plurality of current sensing circuits.10. The electrodeposition measuring system of claim 9, including: aplurality of plastic baffles that are adjustable to alter theelectrodeposition plating currents.
 11. The electrodeposition measuringsystem of claim 9, wherein the computer system further comprises: a dataacquisition board operatively connected to the current probe thatconverts electrodeposition plating currents sensed by the plurality ofcurrent sensing circuits to a plurality of digital values; a computeroperatively connected to the data acquisition board that receives theplurality of digital values provided by the data acquisition board; anda monitor operatively connected to the computer for displaying theplurality of digital values provided to the computer.
 12. Theelectrodeposition measuring system of claim 9, wherein the current probefurther comprises: a conductive layer located on a front face of thecurrent probe; a insulating layer formed adjacent to the conductivelayer; and a plurality of apertures formed through the conductive layerand the insulating layer, wherein each of the plurality of aperturesexposes one of the plurality of current sensing circuits to localelectrodeposition plating currents generated between the electrode andthe current probe.
 13. The electrodeposition measuring system of claim12, wherein each of the plurality of current sensing circuits include: acurrent sensing region, wherein a portion of the current sensing regionis exposed to electrodeposition plating currents by one of the pluralityof apertures formed through the conductive layer and the insulatinglayer; and a conductive line connecting the current sensing region to acurrent measuring device, wherein local electrodeposition platingcurrents incident to the portion of the current sensing region exposedby one of the plurality of apertures is sensed by the current sensingregion and provided by way of the conductive line to the currentmeasuring device.
 14. The electrodeposition measuring system of claim13, wherein each of the plurality of apertures exposes an equal amountof the current sensing regions of the plurality of current sensingcircuits, wherein the amount of the current sensing region exposed andthe current measured by each of the plurality of current sensingcircuits allows local electrodeposition plating current density to bedetermined at each of the plurality of apertures.
 15. Theelectrodeposition measuring system of claim 12, wherein the currentprobe further comprises: an epoxy layer formed adjacent to the pluralityof current sensing circuits, the epoxy layer located on a back face ofthe current monitoring probe, wherein the epoxy layer preventselectrodeposition plating currents incident to the back face of theprobe from affecting the current sensing circuits.
 16. A method ofproviding real time analysis of electrodeposition plating currents, themethod comprising: A. placing a multi-channel current probe in a platingcell; B. generating an electrodeposition plating current; C. measuringthe electrodeposition plating current at a plurality of locations on themulti-channel current probe using a plurality of current sensingcircuits; and D. adjusting the distribution of the electrodepositionplating current based on the measurements taken.
 17. The method of claim16, wherein steps C and D are repeated until the distribution of theelectrodeposition plating currents reaches a threshold level ofuniformity.
 18. The method of claim 16, wherein measuring theelectrodeposition plating current includes determining electrodepositionplating current density based on the electrodeposition plating currentmeasured and a surface area of a current sensing region exposed to theelectrodeposition plating currents.
 19. The method of claim 16, whereinadjusting the distribution of the electrodeposition plating currentbased on the measurements taken includes adjusting a plurality ofplastic baffles.
 20. The method of claim 16, wherein measuring theelectrodeposition plating current includes: sensing theelectrodeposition plating currents at a plurality of current sensingregions; providing the sensed electrodeposition plating currents to adata acquisition board via a plurality of conductive lines; andconverting the sensed electrodeposition plating currents provided to thedata acquisition board to a plurality of digital values representativeof the electrodeposition plating currents sensed at the plurality ofcurrent sensing regions.